In UMTS (Universal Mobile Telecommunications System) networks, Long Term Evolution (LTE) has been specified for the purpose of furthering high-rate data processing, low-latency, and the like. In addition, successor systems of LTE (e.g., LTE-A [LTE-Advanced], FRA [Future Radio Access], 4G, 5G, etc.,) further evolved from LTE have also been studied for the purpose of achieving wider bandwidths and higher rates.
User apparatuses in LTE are classified into multiple categories according to UE (User Equipment) capability. This category is called a “UE category”. For example, a category 6 user apparatus defined in 3GPP Release 10 supports 300 Mbps and 51 Mbps, respectively, as a maximum bit rate (peak rate) of a DL (Downlink) and a maximum bit rate of UL (Uplink). Since 3GPP Release 12 and later, the UE category is defined separately for DL and UL. The UE category of DL is called “UE DL category”, and the UE category of UL is called “UE UL category” (Non-Patent Document 1). The user apparatus UE is defined to report, when accessing, for example, a network, a UE category supported by the user apparatus UE itself to the base station via a predetermined signaling message (UE-EUTRA-Capability).
In LTE, Hybrid Automatic Repeat Request (HARQ) with soft combining is applied. In an HARQ process, when receiving error-containing data, the user apparatus accumulates data in a memory and combines the data with retransmission data to be retransmitted later. Note that the memory used for the HARQ process is called a “soft buffer”. In addition, the base station also performs a data transmission process according to the size of the soft buffer in the user apparatus. Specifically, when performing DL (Downlink) data transmission, the base station performs a rate matching process based on the size of the soft buffer in the user apparatus.